Pamela J. Lein considers whether micro- and nanoplastics are accumulating in the brain and the question of whether they are promoting neurological dysfunction and disease
In February 2025, Nature Medicine published a startling report by a team of researchers at the University of New Mexico that estimated the human brain was 0.5% plastic by weight. This finding was based on their analysis of micro- and nanoplastics (MNPs) in autopsied human brains. Comparative analyses of the MNP levels in human brain, liver, and kidney samples collected in 2016 or 2024 revealed that not only were these tiny plastic particles accessing the brain, but they were actually accumulating in the brain. Specifically, brain samples contained up to 30 times more MNPs than samples from the same person’s liver or kidney.
Further, on average, MNP levels were about 50% higher in samples from 2024 relative to those from 2016, corresponding to the sharp increase in global plastic production during that same time period.
Micro- and nanoplastics research
While some scientists have challenged these findings, subsequent studies have reported similar findings. However, detection of MNPs in the brain does not answer the key question of whether these tiny plastic particles are promoting neurological dysfunction and disease.
What is known is that the biological effects of MNPs vary depending on their chemical and physical properties. Chemically, plastics are complex, highly heterogeneous synthetic materials. Over 98% of plastics are made from fossil carbon, which is used to synthesize carbon-based chains (polymers) composed of smaller repeating units (monomers).
Chemical additives are often integrated into plastic polymers to provide specific properties such as color, flexibility, stability, water repellence, flame retardation, and ultraviolet resistance. As a result, there is a diverse range of different plastics with distinct properties, including polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (Styrofoam). Many of the chemicals added to plastics, including phthalates, bisphenols, per- and poly-fluoroalkyl substances (PFAS), brominated flame retardants, and organophosphorus flame retardants, are known to be toxic to the brain.
The size of plastics is also important in determining their potential to cause harm. Macroplastics are defined as plastics larger than 5 millimeters; microplastics (MPs), between 5 millimeters and 1 micrometer; and nanoplastics (NPs), less than 1 micrometer. Due to their small size, NPs are of particular concern. They are easily transported over longer distances in the environment, can infiltrate deep into tissue and penetrate cellular barriers, and their larger surface area allows for greater adsorption of toxic chemicals.
The MNPs found in human brain tissue by the University of New Mexico researchers were predominantly NPs, primarily polyethylene NPs with lesser but significant concentrations of other plastic polymers.
Do MNPs promote neurological dysfunction and disease in humans?
The possibility that MNPs promote neurological dysfunction and disease in humans was suggested by the authors of the 2025 report in Nature Medicine, who observed a three to five times greater accumulation of MNPs in samples obtained from individuals with a documented diagnosis of dementia at the time of death compared to control patients without. However, as noted by the researchers, it is difficult to determine which came first, the increased particle load in the brain or the dementia, since it is well known that dementia can make the blood-brain barrier leakier, which would be expected to make it easier for plastic particles to move from blood into the brain.
Emerging studies in experimental animal models generally support a potential link between MNPs and dementia, including Alzheimer’s disease. Researchers at the University of Rhode Island found that exposing mice genetically engineered to express human risk genes for Alzheimer’s disease to tiny particles of polystyrene – the plastic used in Styrofoam – significantly worsened memory deficits in these mice. In other studies of fish and rodent models, MNPs have been shown to increase the expression of Alzheimer’s relevant proteins, decrease the number of neurons in the brain, reduce overall brain mass, and cause structural changes in specific brain regions similar to those observed in the brains of humans with Alzheimer’s disease and related dementia.
The Parkinson’s disease link
A recent 2026 review article published in npj Parkinson’s Disease concluded that emerging evidence suggests MNPs may also be fueling the increase in Parkinson’s disease, which has doubled in prevalence over the past 25 years. This conclusion, drawn by a team of researchers from Gannan Medical University and Guangzhou Medical University in China, was based on a review of more than 100 published studies.
A hallmark pathological characteristic of Parkinson’s disease is the aggregation of misfolded α-synuclein in peripheral organs and the brain, and the degeneration of dopaminergic neurons in brain regions that control motor function. As discussed in the npj Parkinson’s Disease review, research in experimental animal and cell culture models has demonstrated that MNPs can accelerate both the initiation and progression of PD by facilitating α-synuclein misfolding and aggregation, and triggering pathological processes that lead to dopaminergic neuronal cell death, including neuroinflammation, oxidative stress, mitochondrial dysfunction, and lysosomal impairment. It remains to be determined, however, whether MNPs are associated with increased risk and/or accelerated progression of Parkinson’s disease in humans.
In summary: Micro- and nanoplastics
In summary, the emerging data provide strong evidence that MNPs readily access the brain, where they tend to accumulate, and that the amount of plastic in human brain tissue is increasing with growing global plastic production and plastic pollution. While there remain significant gaps in knowledge about the impact of MNPs on neurological dysfunction and disease, there is a growing body of experimental data from experimental animal, cell culture, and computational models demonstrating that MNPs promote molecular and cellular changes as well as behavioral changes that are relevant to human neurological disease.
While there are significant uncertainties about the full magnitude of the risks MNPs pose to human brain health, the available data are sufficiently alarming to warrant a concerted societal effort to cut back on how much plastic we make, manage plastic waste more effectively, invent and promote the use of safer alternatives, and help consumers understand the problem and enact personal strategies for reducing plastic pollution.
Relevant references